Industry equipment and most home appliances (which are used in daily life) such as portable devices and office equipment are using electric energy that is supplied from a power plant by cable. To date, a power is being supplied by cable without great inconvenience, but the recent advance and wide use of various portable devices are showing that power supply by cable is not suitable as a power supply source for portable devices. For example, when a portable device receives a power from a battery having a low charge capacity, the battery has a fast recharge period due to the low charge capacity in spite of the enhancement in functions of portable devices. To supplement this limitation, the charge capacities of batteries have increased, but portable devices increase in weight and decrease in portability. Furthermore, in portable terminals which are necessities in daily life, when a battery is completely discharged, it is difficult to charge the battery anywhere. Also, as the use of laptop computers increases, the supply of a power is becoming an increasingly important issue.
As a wireless power transfer (or transmission) technology that wirelessly transfers electric energy from a power source to a desired device, electric motors or transformers using an electromagnetic induction scheme were used from the 1800s. Since then, a method was tried for transmitting electric energy by irradiating electromagnetic wave such radio wave or laser. Electric toothbrushes and some wireless razors are charged by the electromagnetic induction scheme. The kinds of wireless energy transmission schemes are as follows.
First, there is an electromagnetic induction scheme based on magnetic induction. The magnetic induction scheme, which induces a current from a coil to another coil through a magnetic field, has limitations in that a load power and a relative position and distance between the coils are required to be accurate. However, some companies started relaunching new wireless charge devices that charge portable terminals, Personal Digital Assistants (PDAs), MP3 players, and notebook computers by using the electromagnetic induction scheme.
Second, there is a non-radiative wireless transmission technology using a near-field effect. The non-radiative wireless transmission technology is based on an evanescent wave coupling scheme where electromagnetic wave moves from a medium from another medium through a near electromagnetic field when the mediums resonate at the same frequency. A charge station connected to a power source forms the electromagnetic field, and when approaching a portable device, including a receiver that has been designed at the same resonance frequency of MHz band, to inside the electromagnetic field, a kind of energy tunnel is formed between two mediums, thereby charging the portable device within a distance of several m from the charge station. Particularly, such energy is non-radiative and based on a magnetic field, and thus, only when there is a device having a resonance frequency, the energy is transferred to the device, but an unused portion of the energy is spread into the air and reabsorbed into an electromagnetic field. Therefore, unlike electromagnetic wave, the energy does not affect ambient machines and/or human bodies.
Third, there is a long-distance transmission technology using a short-wavelength wireless frequency within an electromagnetic wave range. The long-distance transmission technology uses an electromagnetic radiation scheme using microwave of 5.8 GHz, but is fatal to human bodies.
A wireless power technology according to the present invention is based on the non-radiative wireless transmission technology, and a wireless power transmission apparatus using a magnetic field resonator has a configuration of FIG. 1 generally. When a transmission coil 21 generates a magnetic field with a power generated by an Alternating Current (AC) signal generator 10 and energy is transferred to a transmission resonance coil 22, the transmission resonance coil 22 resonates and amplifies the magnetic field. The amplified magnetic field enables energy to be transmitted much farther than power transmission based on a typical magnetic field induction scheme. Likewise, a reception resonance coil 31 resonates and amplifies a transferred magnetic field, thereby allowing energy to be received efficiently. As a result, energy can be efficiently transmitted to a long distance.
In a magnetic field resonance scheme, however, the resonance frequencies of the transmission resonance coil 22 and reception resonance coil 31 are changed when an ambient environment is changed or an object 50 is located on an energy transfer path. In this case, an energy amplification rate is reduced, thereby affecting energy transmission efficiency in a certain distance.